1. Field of the Invention
The present invention is directed to an x-ray diagnostics installation for radiographs, and in particular to such an x-ray installation having a secondary radiation grid preceding the film holder and means for moving the secondary radiation grid perpendicular to a central ray of the x-ray beam during an exposure.
2. Description of the Prior Art
X-ray diagnostics installation of the type described above are known which include means for forming an electrical signal corresponding to the exposure time, and control means for controlling the speed of movement of the secondary radiation grid dependent on the exposure time, with the speed of movement being fixed.
In x-ray diagnostics installations of this type, the secondary radiation grid has lamellae directed at the focus of the x-ray source for the purpose of suppressing leakage radiation emanating from the examination subject. The movement of the secondary radiation grid during an exposure is intended to prevent the lamellae from becoming visible in the resulting radiograph. In such known systems, the control circuitry for movement of the secondary radiation grid selects a rigidly prescribed rate of speed for such movement. It is not possible, however, using such a fixed speed to prevent grid streaks from becoming visible in the radiograph for all exposure times. As described in German Patent No. 884 148, the speed of the secondary radiation grid is set dependent on the exposure time, however, it is assumed that the exposure time is set before an exposure is actually undertaken, and is thus known. The system disclosed therein cannot undertake an automatic selection of the proper speed of movement of the secondary radiation grid without knowing the exposure time in advance.